Fluorescent lamps are well known in the art and are used for a variety of types of lighting applications. Such lamps are characterized as low pressure arc discharge lamps and include an elongated envelope, whose internal surface is coated with phosphor, an electrode structure at each end of the envelope. The envelope also contains a quantity of an ionizable material, such as mercury, and a fill gas at a low pressure, for example in the order of 1-5 torr. The fill gas can be, for example argon or krypton, or a mixture of these and other gases.
When a voltage is applied across the electrodes, electrons will be emitted, ionizing the gas inside the envelope. The resultant ionization and recombination of ions and electrons produce primarily 253.7 nm. radiation which is converted by means of the phosphor into radiation of a longer wavelength and a spectral distribution, depending on the phosphor material used, in the near ultraviolet or in the visible part of the spectrum.
As stated above, one such lighting application in which fluorescent lamps are used is to provide backlighting to a liquid crystal display. Since the liquid crystal panel itself is a non-luminous element, a light source is necessary for illuminating the liquid crystal panel. The light transmissivity of the liquid crystal panel is controlled according to electrical signals given thereto so that an image corresponding to, for example, a still or moving image is displayed on the liquid crystal panel. A backlit liquid crystal display provides a suitable alternative to the traditional CRT display. When used in conjunction with a dimmable fluorescent backlight, the liquid crystal display device provides a high contrast image over a wide range of ambient light conditions, i.e., from full sunlight to complete darkness.
A typical multi-color liquid crystal display unit comprises a liquid crystal panel, a fluorescent lamp and three individual filters. The coloring is achieved by the deposition of liquid crystal filters on a light-transmissive substrate. This substrate (usually a light-transmissive plate) is typically lit from behind by a fluorescent lamp containing a standard halophosphate phosphor such as daylight. Because of the spectral power distribution from such phosphors, the gamut shape, color balance and brightness of the liquid crystal display is not optimal.
The ideal performance of a liquid crystal color filter would entail 100 percent transmission of light at either 450 nanometers, 540 nanometers or 620 nanometers and 0 percent transmission at the remaining two wavelengths. Hence, a complete display would consist of three individual filters: a blue filter (passing 450 nanometer energy), a green filter (passing 540 nanometer energy), and a red filter (passing 620 nanometer energy), and a fluorescent backlight source which would emit sharp energy peaks at 450, 540 and 620 nanometers.
Examples of fluorescent lamps for liquid crystal displays are described in U.S. Pat. Nos. 4,664,481 and 4,767,193.